The present invention relates to methods for the in situ application of contaminant resistant coatings to papermaking fabrics, and papermaking fabrics so coated. In particular, the invention is directed to methods for the in situ application of nanoparticle coatings to papermaking fabrics that reduce machine down time.
Papermaking fabrics are used in connection with papermaking machines to both form an embryonic web of paper from a pulp slurry and to carry it through various dewatering and drying processes to form various types of paper products. The papermaking fabrics are generally in the form of a fine mesh, which can be of various configurations depending on the position in the papermaking machine, and may include additional layers of batt, for example in certain press and dryer fabrics.
Particles suspended in the primarily cellulose fiber stock used to form the paper may include pitches, adhesives, other glue-like substances as well as other materials that have a propensity to stick to the papermaking fabrics, reducing the fabric permeability and adversely effecting the performance of the papermaking fabric. Prior known solutions to address this problem have proposed coating the fabric with an anti-contaminant material in order to enhance the anti-sticking property of the fabric and maintain the fabric cleaner for a longer period of time after it is installed on a papermaking machine. However, the prior known coatings wear off through use, resulting in diminished performance of the papermaking fabric. Additionally, the thickness of the coating itself had to be very small so that the coating itself did not reduce the fabric permeability.
While initial coatings had a fairly short life, one prior known anti-contaminant coating was developed containing polytetrafluoroethylene (PTFE) that was applied to the fabric using a bath and then cured at a temperature of 200° F. to 400° F. prior to installing the fabric on the papermaking equipment. This anti-contaminant coating had a longer life, but was still subject to wear.
Nanoparticle coatings are also known, such as described in e.g.: WO 02/50191 Solvent-Poor Sol-Gel Systems; U.S. Pat. No. 6,482,525 Method for producing themoshaped substrates coated with a SOL-Gel Lacquer; U.S. Pat. No. 6,620,514 Nanostructured forms and layers and method for producing them; U.S. Pat. No. 6,607,994 Nanoparticle-Based permanent treatments for textiles; U.S. Pat. No. 6,649,266 Substrates produced with a microstructured surface; U.S. Pat. No. 6,629,070 Nanostructured moulded bodies; WO 03/014232A1 Material for producing abrasion proof hydrophobic and/or oleophobic coatings. The generally accepted definition of “nanoparticles” is particles with a size less than about 100 nm. Such coatings have been used in connection with various types of fabric, for example for contamination resistance or to increase wear life. However, they have not been specifically used in connection with papermaking fabrics
In use, it is also known to remove papermaking fabrics having a substantial remaining useful life from a papermaking machine for re-coating and subsequent re-installation in order to maintain the benefit of anti-contaminant coatings. However, this entails substantial additional cost and down time for the papermaking machine.
Thus, it would be desirable if a contamination resistant nanoparticle coated papermaking fabric were available which provided anti-sticking properties when installed in the environment for which it is intended. It would be further desirable if methods existed to allow such fabrics, as well as those not so treated, to be coated or recoated with a either or both a hydrophobic or oleophobic contamination resistant nanoparticle coating while installed in the environment for which they are intended (i.e.: in situ application of the coating). It would also be desirable if methods existed which would allow for in situ application of the contamination resistant hydrophobic and/or oleophobic nanoparticle coating to selected areas only of these fabrics.